(1) Field to which the invention relates
The invention relates to a method and a device for attaching flexible sheets and sheet structures on a base by means of holding means at the corners.
(2) The prior art
Previously conventional methods for fixing relatively large paper sheets such as the use of adhesive tapes or material which is adhesive on both sides or fixation with drawing pins suffer from the disadvantage that when the temperature or atmospheric humidity changes, as may often occur, the different extension or contraction of the paper on the one hand and of the base on the other hand cannot be compensated for.
The effects and counter-measure taken in this respect are as follows:
When hung on the wall decorative posters and other large pictures quickly assume an uneven or wrinkled appearance and therefore make a poor general impression. On contraction of such decorative posters the strains occurring may be so pronounced that the adhesive tapes are detached and such posters fall from the wall, or on the other hand, the poster may be torn. Sometimes the posters are provided at the top and bottom edges with stuck on or clamped on rails or moldings and so hung on the wall with the result that the lower molding is suspended freely and under the action of gravity the bottom rail ensures that the poster remains more or less flat. Whether such a way of pinning up posters so that they may be caused to flutter by air currents is however a matter of taste.
Advertising posters as used in shop windows, used for drawing attention to special offers or other matters concerned with a momentary boost in sales, are usually only stuck to the window by means of adhesive applied to the surface of the poster. This offers the disadvantage that when the posters are to be changed it is always necessary to wash off the remains of adhesive. The work required and the awkwardness of using water for washing the window discourage more especially the owners of small businesses from attaching posters in this manner at all.
Drawing paper fixed to drawing boards often becomes loose and forms corrugations owing to expansion and therefore has to be drawn tight again. The frequent undoing of adhesive tapes, necessary for this purpose, on the one hand and the temporarily occurring substantial thrust stresses in the adhesive layer on the other hand (on contraction of the paper) lead to the drawing board being considerably fouled with adhesive at positions adjacent to the corners of the sheets.